1. Field of the Invention
The present invention relates to a technique of generating a motion image of a first object in a virtual space where the first object and a second object are present, in accordance with a positional relationship between the first object and the second object.
2. Description of the Related Art
In three-dimensional video games, a motion image of an object like a character which is present in a virtual three-dimensional space is generated by performing perspective transformation on the range of the virtual three-dimensional space including the object with a virtual camera. In such three-dimensional video games, in addition to a player character that takes a motion according to an operation of a player, many other objects like enemy characters who play against the player character are present in the virtual three-dimensional space.
When many other objects are present in a virtual three-dimensional space, the motion of an object may be affected by external forces, such as, for example, one applied from another object. Japanese Patent Laid-Open Publication No. 2003-62326 and Japanese Patent Laid-Open Publication No. 2003-67773 disclose a scheme of changing the individual blend ratio of motion data of a first object (e.g., a weapon owned by a player character) for each bone set for the first object when the first object hits a second object (e.g., an enemy character). This makes it possible to generate an image that is reproduced in accordance with an influence originating from external force applied to an object from another object.
When another object is present, however, the actions of human beings and animals are affected by the object even though no external force is directly applied therefrom. For example, human beings may take an action while observing an object, such as, for example, chasing a ball in a ball game. Moreover, human beings may change a direction, for example, while walking to avoid an obstacle (such as, for example, an object). Such a human action that is affected by another object is often performed subconsciously.
An operation pad of a game machine through which a player (or user) inputs an instruction for a character to take a motion has a limited number of directional keys for inputting a direction, and a limited number of buttons for inputting individual instructions. Thus, the kinds of inputtable instructions are limited. This makes it impossible for the player (or user) to input a different instruction due to the presence of another object. When the player instructs the same motion, the character may take the same motion regardless of where the other object is.
If the kinds of instructions inputtable through the operation pad increase, when an instruction is input, it becomes difficult for the player to intuitively determine how the character takes a motion, or what positional relationship another object has set with respect to the character. An increase in the kinds or instructions inputtable through the operation pad may frequently result in making an erroneous input of an instruction not intended by the player, or may delay inputting of the player's instruction. Apparently, an increase in the kinds of the instructions inputtable through the operation pad makes a game too complex.